Trocar tubes used in laparoscopic surgery are normally fitted with a gas-tight seal to maintain pneumoperitoneum when a laparoscopic instrument is inserted into the trocar tube. The gas-tight seal is normally built into the rear housing attached to the cannula of the trocar tube, and forms a gas-tight seal with an instrument having an outside diameter that is similar to the internal diameter of the cannula.
In the course of laparoscopic surgery, it is often necessary to insert into the trocar tube a laparoscopic instrument having a diameter that is less than the diameter of the cannula. The gas-tight seal built into the trocar tube cannot provide an adequate gas-tight seal with such a smaller-diameter instrument since known gas-tight seals suffer from an inability to accommodate a wide range of instrument diameters. Known gas-tight seals leak when a smaller-diameter instrument is inserted, and/or impose excessive friction when a larger-diameter instrument is inserted. Known gas-tight seals also have an increased tendency to leak with a smaller-diameter instrument when the instrument is displaced laterally.
In known gas-tight seals, a thin, circular piece of an elastic material is rigidly supported at its periphery. In the center of the elastic material is a circular instrument port through which the instrument passes. The elastic material surrounding the instrument port contacts the instrument, which forms the gas-tight seal. The inability of known gas-tight seals to seal with instruments having a large range of diameters results from this basic construction.
The instrument port must be smaller than the diameter of the instrument so that the instrument can deform the elastic material surrounding the instrument port to form the seal with the instrument. Consequently, when the seal is to accommodate a range of instrument diameters, the instrument port must be smaller than the minimum of the range of instrument diameters for which the seal is designed, so that a minimum-diameter instrument can deform the elastic material. Deforming the elastic material results in a radial force between the elastic material and the instrument. This holds the elastic material in contact with the instrument and maintains the gas-tight seal.
An instrument port diameter that produces the required amount of radial force for a minimum-diameter instrument results in a greater radial force when a larger-diameter instrument is inserted. The greater radial force increases friction between the seal and the instrument. With known gas-tight seals, the maximum of the diameter range, above which friction is so great as to make it impossible to manipulate the instrument, may not be a great deal larger than the minimum of the diameter range, below which the gas-tight seal leaks.
In known gas-tight seals, the radial force between the elastic material and the instrument at the minimum of the diameter range must be increased if the instrument is to be allowed to move laterally in the seal. The increased radial force is required to keep the elastic material remote from the direction of lateral displacement in contact with the instrument, and thus to maintain the gas-tight seal. This increase in the radial force further increases friction between the seal and the larger-diameter instrument, and thus further limits the diameter range that the seal will accommodate.
To enable instruments with a range of diameters to be used in the same trocar tube, and to form a gas-tight seal with instruments having a range of diameters, it is known to fit a trocar tube with an auxiliary gas-tight seal. The auxiliary gas-tight seal supplements the diameter range capability of the main gas-tight seal. For example, the applicant's assignee sells trocar assemblies in which the trocar tube has a 10 mm (0.4″) diameter cannula that can accommodate instruments ranging from 5 mm (0.2″) and 10 mm (0.4″) in diameter. The trocar tube accommodates this range of diameters by providing two auxiliary door-type gas-tight seals in addition to the main gas-tight seal. The main gas-tight seal, which will be described further below, seals with instruments between 9 and 10 mm in diameter; a first auxiliary seal seals with instruments 7 to 8 mm in diameter, and a second auxiliary seal seals with instruments 5 and 6 mm in diameter.
The two auxiliary door-type gas-tight seals are stored on opposite sides of the rear housing of the trocar tube. Each auxiliary seal is mounted in a track that runs up the side and across the rear face of the housing. Before a smaller-diameter instrument is inserted into the cannula, the surgeon must slide the appropriate auxiliary gas-tight seal up the track from the storage position into place on the proximal face of the housing. In this position, the auxiliary seal forms a seal with a lip on the main gas-fight seal, and seals with the smaller-diameter instrument passed through it. If another instrument with a different diameter is later to be inserted into the cannula, the one auxiliary seal must be returned to its storage position, and, if necessary, the other auxiliary seal deployed.
Time is needed in the operating room to move each auxiliary gas seal back and forth from its storage position to its operating position. The process of sliding the auxiliary gas-tight seal can be tedious, especially for gloved hands. The surgeon must remember, or double check, which auxiliary seal is in place before inserting an instrument into the trocar tube. If the auxiliary seal is too large for the instrument, the seal will leak; if the auxiliary seal is too small for the instrument, there will be excessive friction between the seal and the instrument. With an extreme diameter mismatch, the instrument can tear the seal, which would then require that the trocar tube be replaced.
As an example of a different approach to accommodating in a single trocar tube instruments with a range of diameters, U.S. Pat. No. 5,104,383 describes a completely detachable auxiliary seal that allows an instrument as small as 5 mm in diameter to be used in a 10 mm cannula. The auxiliary seal is installed into the rear of the housing before a smaller-diameter instrument is inserted into the cannula. A single auxiliary gas-fight seal is made to accommodate instruments with a range of diameters by including a rigid stabilizer plate to prevent the instrument from being moved laterally relative to the cannula. The stabilizer plate keeps the instrument centered in the cannula, and prevents gas leaks caused by the instrument going off center in the auxiliary seal.
Thus, with known auxiliary gas-tight seals, either a single, wider range, auxiliary gas-tight seal or plural, narrower-range, auxiliary gas-tight seals can be used to accommodate instruments with a range of diameters. If plural, narrower-range, auxiliary gas-tight seals are used, the surgeon has to ensure that the auxiliary gas-tight seal is the appropriate one for the diameter of the instrument being used. If a single, wider-range auxiliary gas-tight seal is used, the surgeon must accept that the range of lateral movement of the instrument in the cannula is limited if the auxiliary gas-tight seal is to seal effectively with an instrument at the minimum of the diameter range.